1. Field of the Invention
This invention relates to a molded article of a pen tip of an input pen for a coordinate input apparatus, a mold for molding the pen tip and a method of molding the pen tip.
2. Related Background Art
As a coordinate input apparatus, there is known one which detects elastic wave oscillation input from an input pen by a plurality of sensors provided on an oscillation transmitting plate, and detects the coordinates pointed to by the input pen. The tip of the input pen of such a coordinate input apparatus is described, for example, in Japanese Patent Laid-Open Application No. 1-114924. The pen tip described in this patent application is formed of polyamide-imide, which is a resin, and has satisfied the characteristics
(1) that it is excellent in wear resistance and resists wear due to friction or the like during the inputting of coordinates, and
(2) that it can transmit oscillation created in the input pen efficiently without attenuating the oscillation.
However, the tip of the input pen of the above-described prior-art coordinate input apparatus has used polyamide-imide, which is a resin, as the material thereof and therefore has been made moldable and has been expected to be capable of being made into a construction excellent in mass production, but the following problem has arisen in the tip of the molded input pen.
When an input pen incorporating the molded tip therein has been brought into contact with an oscillation transmitting plate perpendicularly thereto and the input pen has been rotated about the axis of the input pen, there has been found a phenomenon that the waveform of a signal detected by the sensor changes. That is, when the oscillation input from the input pen propagates in the form of a ripple from an input point on the oscillation transmitting plate as the center of the ripple, there arises a phenomenon that the waveform of the detected signal differs depending on the direction of the input pen. This phenomenon is called directionality, and has harmful effects as will be described below.
In the prior-art coordinate input apparatus, it is the basic principle to derive a distance by the use of the transmission time of a sound wave and the sound velocity of a wave and therefore, it is of course desired that the sound velocity be constant in a propagating body and that a detection signal waveform detected by the sensor always be of the same shape. That is, even if as shown in FIG. 8 of the accompanying drawings, oscillation is input at the same point, the detected propagation time will differ if the detected signal waveform differs. That is, in FIG. 8, propagation delay time 1 and propagation delay time 2 have vibrations input at the same point, and therefore, originally the same values must be detected, but the two values will differ from each other if waveform deformation occurs due to some factor. As a result, the coordinate input apparatus will effect wrong detection as if it detected oscillation input from different points. This means a degradation in the accuracy of the coordinate input apparatus. Accordingly, in order to realize a highly reliable coordinate input apparatus, there is required such a construction that can always detect the same detection signal waveform.
As described above, the generation of the directionality of the input pen reduces the accuracy of the coordinate calculation of the coordinate input apparatus of this kind, and in order to realize a highly accurate and highly reliable coordinate input apparatus, there is required some countermeasure.
The present invention has been made in view of the above-noted problem and has as its object to provide a molded article of the tip of an input pen for use for the inputting of the coordinates of a coordinate input apparatus which can mitigate the generation of the directionality thereof, and a coordinate input apparatus.
In an embodiment of the present invention, there is provided a molded article of the tip of an input pen for a coordinate input apparatus for inputting an oscillation to an oscillation transmitting plate, detecting an oscillation propagating the oscillation and detecting indicated coordinates, characterized in that the molded article is molded by injecting a composition containing at least liquid crystalline resin into a mold member for molding the configuration of the pen tip.